Calibration of Resistance Factors for Load and Resistance Factor Design of Internal Limit States of Soil Nail Walls

Abstract

A general approach for calibration of resistance factors for load and resistance factor design (LRFD) of pullout and tensile failure internal limit states of soil nail walls is presented. The calibration of resistance factor values includes the influence of nominal load and nominal resistance model type and accuracy (method bias), bias dependencies, uncertainty in nominal load and resistance values, and possible cross-correlation (dependency) between nominal load and resistance terms. The current default Federal Highway Administration simplified method and an improved version are used to compute maximum nail loads under operational (in-service) conditions. Nail pullout capacity is calculated using the effective stress method adopted in Hong Kong and a more accurate modified version. Resistance factors are calibrated for a range of load factors and target reliability indexes. Example design outcomes for internal limit states of a soil nail wall using different load and resistance model combinations are presented. The benefit of using the more accurate improved load and resistance models for soil nail wall pullout design is demonstrated by a reduction in total length of soil nails.